U.S. Pat. No. 4,874,643, issued on Oct. 17, 1989 to Susan L. Oldham et al and assigned to Hughes Aircraft Company, the teachings of which are incorporated herein by reference, describes a method for rendering a substrate resistant to erosion by a plasma comprising oxygen, and by other erosion phenomenon (for example, rain erosion and plastic media blasting paint removal operations). The erosion resistance is rendered by providing on the surface of the substrate a coating of a cured polymer of a compound having the general formula ##STR4## where: R.sub.1 is selected from the group consisting of:
(a) an aliphatic hydrocarbon group containing 2 to 10 carbon atoms; and PA2 (b) a group having the formula ##STR5## wherein n=1 to 3,
m=0 to 5, PA1 R.sub.2 and R.sub.2 ' are each selected from the group consisting of an alkyl group containing 1 to 4 carbon atoms, an unsubstituted aryl group, and a substituted aryl group, and R.sub.3 comprises ##STR6## where n=0 to 10. PA1 n=0 to 10.
U.S. Pat. No. 4,861,901, issued on Aug. 29, 1989, to Kreisler S. Y. Lau et al and also assigned to Hughes Aircraft Company, the teachings of which are incorporated herein by reference, provides an additional R.sub.3 moiety, to wit, ##STR7## where R.sub.4, R.sub.5, and R.sub.6 are each selected from the group consisting of H, an alkyl group containing 1 to 4 carbon atoms, and an aryl group, and where
A preferred compound is 1,8-bis(m-glycidylphenyldimethylsilyl)octane or 1,8-octanediylbis (dimethyl(3-(oxiranylmethyl)phenyl)silane; the name given to this compound in the above-identified patents is 2,11-bis(3-glycidylphenyl)-2,11-dimethyl -2,11-disiladodecane (CAS 120390-91-2). Herein, this compound and its analogs will be referred to by the first of the above three names, namely, the octane. In any event, in formula (I) above, R.sub.1 is an aliphatic hydrocarbon group containing 8 carbon atoms, R.sub.2 and R.sub.2 ' are each --CH.sub.3 and n in R.sub.3 is 1. The resulting formula is ##STR8## also called HRG-3.
However, while this patent is suitable for its intended purpose, the present inventor has found that HRG-3 is difficult to formulate into a coating that can be easily cured at room temperature. Even when formulated with very reactive epoxy diluents and amine curing agents, full cure occurs at room temperature only after 72 hours. In addition, one of the synthetic intermediates, 3-allylbromobenzene, is difficult to make and employs expensive starting materials. Yields have been found to be low and difficult to improve for this intermediate. Also, this intermediate material is very difficult to purify.
Thus, what is needed is an erosion-resistant coating that employs a less expensive intermediate, is easier to prepare, and cures at room temperature in a matter of hours, not days, while retaining most, if not all, of the advantages of the prior art coating.